|The UN Security Council has already called on Libya for an immediate end to violence against protesters [Reuters]
The US is to impose unilateral and multilateral sanctions on Libya, the White House has announced.
US spy agencies are also monitoring Libya for evidence of atrocities, Jay Carney, the White House spokesperson, announced on Friday.
He declined to give details of what the sanctions might entail in a press conference in Washington.
Washington has withdrawn embassy personnel from the Libyan capital and suspended all embassy operations for security reasons, Carney said.
The embassy has temporarily ceased all operations, he said.
Diplomatic personnel had been ordered to leave the country earlier this week. A US-chartered ferry carrying at least 167 American citizens and 118 other foreigners arrived at the Mediterranean port of Malta on Friday, after being held up by bad weather in Tripoli for two days.
The UN Security Council began discussions on the situation in Libya in New York, with sanctions and the possible imposition of a no-fly zone over the country under Chapter VII of the UN charter on the table.
Ban Ki-moon, the UN Security General, called on the council’s members to take "decisive action" on the Libya crisis.
He said reports indicate at least 1,000 people have been killed.
"Colonel Gaddafi's supporters are reportedly conducting house-by-house searches and arrests; according to some reports, they have even gone into hospitals to kill wounded opponents," he said.
He underlined the importance of offering support to Libyans seeking refuge from the violence, highlighting the 22,000 people who have already fled to Tunisia. Another 15,000 have crossed the border into Egypt, he noted.
Ban also said he had called on European countries to keep their borders open to the migrants fleeing the violence.
Al Jazeera's correspondents at various locations on the Libyan border confirmed that the flow of migrants accelerated on Friday afternoon, following violence in the capital and the west of the country.
Ban is scheduled to meet with Barack Obama to discuss possible actions to be taken to stop violence on Monday, the White House's spokesperson said.
"He will also discuss the range of activities that UN agencies and the international community can undertake to address the significant humanitarian needs created by this crisis," Carney said.
Earlier on Friday, the UN's top human rights official said reports of mass killings in Libya should spur world leaders to "step in vigorously" to end the violent crackdown in Libya, and that the 47-nation body should use "all means possible".
Friday's session in Geneva was the first time that the UN Human Rights Council has held a special session to discuss actions against one of its members, with Navi Pillay, the UN High Commissioner on Human Rights, giving support for an independent panel to investigate the alleged abuses by Libyan security forces.
"Today's brutal and shocking situation is the direct outcome of a callous disregard for the rights and freedom of Libyans that has marked the almost four-decade long grip on power by the current ruler," she said.
"Any official, at any level, ordering or carrying out atrocities and attacks can be held criminally accountable.''
Nick Spicer, Al Jazeera's correspondent in Geneva, said the commissioner questioned if there had been crimes against humanity taking place, terminology which would set the legal framework for any future action.
Meanwhile, the Libyan envoy to the UN told the session on Friday that the mission in Switzerland had quit, and employees at the embassy now "represent the Libyan people".
Tripoli's ambassadors to France, Portugal and to the UN cultural and education organisation (UNESCO), also resigned on Friday, adding to the growing number of diplomats quitting over the crisis.
NATO also issued a brief statement, saying they would "continue to monitor the situation in coordination with other international organisations", and would be prepared "for any eventuality".
Tim Friend, reporting for Al Jazeera from outside NATO headquarters in Brussels, said that much of what the military organisation is capable of - such as providing troops - would have to be sanctioned by the UN before any action coud take place.
The developments came hours before a UN Security Council in New York meeting that will consider actions, including sanctions, against the government of Muammar Gaddafi.
David Cameron, the British prime minister, warned Libyan authorities "the world is watching you, and the world will hold you to account".
"International justice has a long reach, and a long memory," he said.
European nations have led the call for a UN-led investigation into possible war crimes and the use of sanctions against Libya.
France has already urged the body to approve a draft resolution that calls for a "total arms embargo, sanctions and asking the International Criminal Court to proceed over crimes against humanity".
Guido Westerwelle, the German foreign minister, said his country was also preparing sanctions, including travel bans and asset freezes on Gaddafi's family, but dismissed economic sanctions on the country as a whole.
Cameron discussed the possibility of "multilateral measures" against Libya with Barack Obama, the US president, earlier in the week.
David Owen, Britain's former foreign minister and a current member of the House of Lords, said the UN will need to play a humanitarian role in feeding people and helping with medical assistance, as civil society in Libya breaks down and basic services come to a standstill.
UN forces may need to go in to protect the humanitarian convoys, a role.
"That would be better done by Egyptian and Tunisian forces," he said, arguing that, despite the problems being faced by the two neighbouring countries following their own recent uprisings, it is important for the Arab world to play a leading role in responding to the Libyan crisis. Arab support could help discourage Russia from using its veto against intervention in Libya, he argued.
He said it while would not be possible to put troops on the ground in the context of a situation that is edging closer to civil war, the international community could intervene to close Libya's airspace.
"We can't put troops on the ground into a civil war… all we can do is to try and help those people not be attacked from the air by those forces," he said.
China and Russia, traditionally reluctant to interfere in the internal affairs of other countries, have supported a statement from the security council issued on Tuesday that condemned "the repression against peaceful demonstrators,'' and demanded an "immediate end to the violence".
Charles Nduka Onianwa, Nigeria's ambassador to the UN rights council, said it was "obvious ... that the indiscriminate use of force against peaceful protesters should be condemned".
Pakistan also said the 57 members of the Organisation of the Islamic Conference "condemn the use of force".
"Muslims will no longer tolerate inequalities and injustice,'' he told the council on Friday.
"A new dawn has come. The rules of the game have changed. Those who do not embrace it will be swept away."
However Hugo Chavez, the Venezuelan president, appeared to write on social networking site Twitter that the Libyan unrest was a "lesson" for right wing governments in the West.
"Long live libya. Long live the independence of Libya," he wrote, saying Gaddafi faced a civil war.